//响应时长
module.exports= function () {
    return function (req,res,next) {
        var start=Date.now();
        var end=res.end;
        res.end= function (chunk, encoding) {
            res.end=end;
            res.end(chunk,encoding);
            console.log('响应时长：(',Date.now()-start,'ms)',req.method,req.url);
        };
        next();
    }
};